The subject of the present invention is a Venetian blind comprising a winding shaft, on which is mounted at least one winding drum, on which is wound a cord fastened to the lowermost slat of the blind and passing through the other slats in their middle part, and a slat orientation mechanism comprising a pulley frictionally driving a flexible ladder, the ends of the sides of which are connected to two bands fastened to each of the edges of the slats in order to ensure that these slats tilt into the closed position when the blind is completely unwound, and a movable member positioned elastically and subjected to the action of the cord under the effect of the pull exerted on the cord by the lowermost end slat, this movable member controlling stop means keeping the slats in a first inclination when they are operative and allowing the slats to tilt into a second inclination when they are inoperative.
A blind of this type is known from the patent DE 3,205,491. In this blind, the movable member consists of a pusher mounted at the end of an elastic arm parallel to the axis of the pulley and bending under the pressure of the cord wound on the pulley. This pusher acts on a slide forming a retractable stop for one of the ends of a helical spring of a friction-spring clutch, the slackening of the cord having the effect of retracting this stop and allowing the clutch to ensure that the ladder is driven at an angle determined by a stationary stop. The orientation mechanism comprises approximately seven parts and it is not symmetrical, that is to say it can be used only in a single direction of rotation.
An orientation mechanism of the same type as the abovementioned mechanism is also known from the patent application DE 3,037,701. However, there, the control of the spring of the clutch is obtained in an appreciably more complicated way, with the result that the mechanism comprises between fifteen and eighteen parts.
The patent application EP 0,050,677 discloses, furthermore, an orientation mechanism which likewise comprises a bar elastically mounted parallel to the axis of the winding pulley and subjected to the action of the cord, this bar being equipped with two radial pawls which drive the inner side of the ladder by means of a driver fastened to this side, thereby causing the slats of the blind to tilt into the closed position when the bar is relieved. The bar also serves as a means for coupling the drum of the ladder to the winding pulley. This mechanism comprises approximately seven parts and it is not symmetrical.
These three mechanisms moreover have the common characteristic of possessing parts which work radially, thus limiting the diameter of the drive shaft and making it virtually impossible to mount the mechanism on a tubular motor. Furthermore, the asymmetry of these mechanisms makes it necessary to take special precautions for the orientation of the mechanism during the assembly operation.